Microbiome-Induced Effects on Root Architecture in Rice Crops: Mechanisms, Drivers, and Functional Consequences

Bacteria play an important role in addressing challenges in rice production by promoting plant growth and enhancing stress tolerance through multiple mechanisms. Different types of soil bacteria affect rice growth by improving nutrient absorption, managing stress, and enhancing root structure. The relationship between rice plants and bacteria is intricate, as these bacteria can help reduce problems like salt stress, heavy metal toxicity, and infections. This review summarises studies published up to 2025 on how bacteria influence rice roots, including aspects like root length, density, biomass, and volume. Bibliometric analysis shows an increase of over 900% in research interest after 2020, with most studies conducted under controlled conditions and limited field validation. In addition to identifying key bacterial groups such as Bacillus, Pseudomonas, Burkholderia, and Azospirillum, this review identifies research gaps related to context dependency, strain specificity, and scalability. We have also emphasised the need for multi-strain inoculation strategies, field-scale experiments, and integration of microbial selection with rice breeding. The synthesis has highlighted that bacterial strains do not simply stimulate root growth but actively reprogram rice root architecture, modulating elongation, branching, density, and surface area as a response to environmental constraints. These effects are mediated by interconnected mechanisms that include phytohormone production, nutrient solubilisation, deaminase activity, stress-related gene regulation, and microbiome-driven feedback involving root exudation. Overall, viewing bacteria as regulators of root developmental dynamics rather than simple biofertilisers provides new insights for designing climate-adapted and sustainable rice production systems.